Throughout the life of a spacecraft, attitude modifications are made to carry out mission objectives, to determine orientation, and to correct for undesired torques. In order to minimize expendable fuel in slewing maneuvers, reaction wheel systems are used to transfer rotational momentum to and from the satellite body.
In certain maneuvers such as, for example, sun acquisition, large attitude changes impose tremendous challenges upon a reaction wheel system due to the sun acquisition time constraint as well as the wheel momentum saturation. If wheel saturation occurs during slew maneuvers, the path actually traced by the spacecraft will differ from the ideal path. This may result in failure to acquire the sun. If a fixed slew rate is used to perform the maneuver, the rate must be slow enough not to saturate the reaction wheel system throughout a wide range of initial momentum states. This may lengthen the sun acquisition time significantly and fail to meet the power safe time constraint requirements.
What is needed is a method and system for determining slew rate and direction that will avoid momentum wheel system saturation while generating maximum maneuver rates so that acquisition time limit requirements can be met. The spacecraft should be able to perform the maneuver autonomously.